Alcohol addiction is a complex psychiatric disorder that can benefit from better understanding of the underlying neurobiological signaling mechanisms. Our preliminary data show that chronic intermittent ethanol exposure significantly increases dendritic spine density in the nucleus accumbens (NAc). Concurrent with the increase in spine density, we observed an increase in glutathione-S-transferase Pi (GSTP), an enzyme is responsible for the forward reaction of the post-translational thiol modification, S-glutathionylation, on redox sensitive cysteine residues of dendritic spine proteins. Such proteins include cofilin, Arp2/3, G-actin and F-actin that mediate actin cycling in response to dendritic spine plasticity. We also found that genetic deletion of GSTP increases dendritic spine density and voluntary alcohol consumption in mice, implicating GSTP-mediated S- glutathionylation as a regulatory mechanism of dendritic spine plasticity and alcohol drinking. The primary hypothesis of this proposal is that voluntary alcohol drinking and dendritic spine plasticity are inhibited by GSTP-induced S-glutathionylation of redox sensitive actin cycling proteins in the nucleus accumbens. This study will therefore substantially increase our knowledge regarding the contribution of this enzyme to the underlying neurobiology of human alcohol addiction. Moreover, the regulation of alcohol addiction by S-glutathionylation is innovative and completely novel to the field. To accomplish this goal, voluntary drinking behavior will be quantified in C57BL/6J mice after treatment with carnosic acid, which increases GSTP expression, thereby establishing a role for GSTP as a novel therapeutic target to treat alcohol use disorders. In addition, C57BL/6J, GSTP WT and GSTP KO mice will be used together with adeno-associated virus (AAV)-mediated GSTP overexpression and knockdown to quantify specific S-glutathionylated actin cycling proteins and dendritic spine morphology in the NAc in a model of voluntary ethanol consumption. Moreover, voluntary drinking behavior will be quantified after inhibition of NAc dendritic spine plasticity through inhibition of actin polymerization. This will e achieved with the following specific aims. Aim 1: Determine if GSTP activators alter S-glutathionylation of spine proteins and reduce drinking in C57BL/6 mice. Aim 2: Using a combination of genetic and in vivo viral approaches, we will determine the role of GSTP in functional and morphological adaptations of dendritic spines and actin cycling proteins in the NAc in mouse models of voluntary ethanol consumption. Aim 3: Determine if inhibition of actin polymerization and dendritic spine plasticity reduces drinking in GSTP WT and KO mice. The expected overall impact of this innovative proposal is that our findings point to this enzyme being a vulnerability factor in alcohol addiction. These data will also provide evidence to support GSTP as a novel therapeutic target to treat alcohol use disorders.